One member of Angela's Merkel's party has suggested that US agents should be expelled from Germany. Photograph: Andy Wong/AP

The White House was forced to defend its increasingly fraught relationship with Berlin on Monday as the Central Intelligence Agency maintained a conspicuous silence about new allegations linking it to a spying scandal involving a German intelligence official.

Reuters quoted two US officials, speaking on condition of anonymity, who told the news agency that the CIA was involved in the alleged recruitment of the official, a 31-year-old employee of the German intelligence agency (BND).

The official was arrested on Wednesday on suspicion of having sold secret documents to a contact at the CIA.

The controversy has threatened to upend an uneasy, monthslong diplomatic rapproachement between the two allies after chancellor Angela Merkel revealed the National Security Agency had monitored her cellphone, causing widespread outrage in Germany and even on Capitol Hill. President Barack Obama was prompted to pledge an end to spying on the leaders of allied nations.

But a longstanding reluctance to discuss intelligence matters in public left the administration scrambling to respond.

The White House spokesman, Josh Earnest, said he could not comment on the arrest of a suspected US spy because it did not want to interfere in “a pending German law enforcement investigation” and because “it obviously goes to, purportedly, a direct intelligence matter as relates to the United States.”

But Earnest appeared to acknowledge that the suspicion alone may have already caused damage to its relationship with Berlin and sought to reassure its ally about the longer term relationship between the two countries.

“The relationship the US has with Germany is incredibly important,” said Earnest, insisting it was a partnership “built on respect” and “decades of cooperation and shared values”.

“All those things are high priorities not just of this administration but of this country, so we are going to work with the Germans to resolve this situation appropriately,” he said during the White House's daily briefing with reporters.

Germany was reported on Monday to be considering stepping up its counter-espionage efforts in light of the affair. Measures being considered in response to the scandal include monitoring the intelligence activities of nominal Nato allies such as the US, Britain and France, as well as expelling US agents from Germany.

According to a report in Bild, the interior minister, Thomas de Maizière, has emphasised the urgent need for a "360-degree vision" of the foreign secret agency's activities. The newspaper claims to have obtained an internal document which outlines "concrete counter-measures", moving away from a policy of not spying on Nato allies.

Asked about the new policy, a spokesperson at the German interior ministry did not deny the reports and said "an efficient and effective counter-intelligence against all sides is important, necessary, and has to be better organised than it has until now."

The BND staffer, a technical support worker employed in a unit dealing mainly with the protection of German soldiers abroad, is alleged to have established contact with the American secret service by contacting the US embassy. Rather than report the contact to their allied German counterparts, the CIA is reported to have paid the agent €25,000 ($34,000) for 218 documents classified as confidential or top secret.

In a press conference on Monday, government officials declined to comment on the affair, but a number of high-ranking politicians and officials have expressed their outrage, with one member of Merkel's party suggesting that US agents should be expelled from Germany.

"If it emerges that the BND employee was really directed by American agents on German soil, then it would be hardly comprehensible if US employees could continue to do harm over here," Karl-Georg Wellmann of the CDU told Spiegel Online.

The German president, Joachim Gauck, said if the allegations turn out to be true, it would amount to "gambling with friendships and close alliances".

"Then it truly needs to be said: enough is enough," he added.

Merkel has been more guarded in her reaction, telling a news conference during her current trip to China: "If the reports are correct it would be a serious case."

In Washington, the administration’s discomfort was evident. Earnest was even forced to clarify that his brief comments on the subject should not be taken as a denial of US involvement in the affair. Initially asked whether Merkel was right to warn that the allegations, if proven, would be a “clear contradiction of trust between allies”, Earnest replied: “That's obviously a big 'if'.”

But when asked whether this was effectively a qualified denial of the claim, the US spokesman was forced to backpedal and make clear the White House was saying nothing to dispute the allegations at the this stage.

“That's not what it was,” clarified Earnest. “It was an observation about a question which was predicated entirely on a hypothetical – not that it was an unreasonable question.”

The CIA refused to make any comment about its alleged involvement in the latest spy-fueled rift between the US and Germany. A spokesman, Ryan Trapani, would not even discuss whether agency director John Brennan had, as Reuters reported, requested to brief Congress on the subject.

Notably, Trapani did not deny a CIA role.

Capitol Hill sources were unaware Monday of any briefing Brennan had offered to give legislators – often a method to defuse congressional tension or outrage ahead of a burgeoning scandal, particularly by the spy agencies.

Any such briefing would come at a delicate time for Brennan. The director has all but burned his bridges with the Senate intelligence committee a little more than a year into his tenure, thanks to ongoing acrimony over a congressional inquiry into the CIA's post-9/11 torture apparatus. The Obama administration is currently awaiting partial declassification of the panel's years-long inquiry, following a censorship process led by the CIA itself.

Another difficulty for Brennan with Congress is the opposition the panel's chairwoman, Democratic senator Dianne Feinstein, has voiced concerning spying on the US's ostensible partner in Berlin. Last year, Feinstein thundered against the NSA monitoring Merkel, even as the senator remained a staunch supporter of most other NSA surveillance, to include its domestic operations.

The US state department defends US-German relations after a top US intelligence official was asked to leave Germany on Thursday in connection with investigations into suspected US spying in the country